A drain pan for receiving and discharging drain water to the outside is provided in the lower portion of heat exchangers in general-purpose air conditioners.
Drain water held in a drain pan is discharged to the outside through a drain pipe from an inclined trench provided in the drain pan in the case of window type and wall type air conditioners, and through a drain pipe after being pumped up by a drain pump (including drain up kits) in the case of ceiling embedded-type and ceiling suspended air conditioners.
In either case, however, drain water stays in the drain pan for a predetermined period of time. Therefore, bacteria can multiply in the drain water in the drain pan, and odor and clogging of the drain pipe due to generation of slime become a problem.
As a measure against this, a technology for layering an antibacterial agent-containing resin composite layer and a sheet or a film made of a resin on the inner wall surface of the drain pan in sequence has already been proposed (see Japanese Laid-Open Patent Publication No. 10-78240). The antibacterial agent-containing resin composite layer contains crystal polypropylene, an inorganic filler and an antibacterial agent. Thus, according to this technology, the antibacterial agent transmits through the sheet or the film made of a resin and acts on the drain water, and therefore, bacteria are prevented from multiplying in the drain water.
In addition, a technology for pasting a copper alloy foil having pasteurizing effects on the bottom of the drain pan has also been proposed (Japanese Laid-Open Patent Publication No. 2-106630). Furthermore, a technology for mixing a pasteurizing agent in the material that forms the drain pan and irradiating the drain water with ultraviolet rays from an ultraviolet ray lamp has also been proposed (Japanese Laid-Open Patent Publication No. 2000-97447).
In any of the above described technologies, however, a problem arises in that the structure of the drain pan becomes complicated, and the bacteriostatic effects gradually decrease together with contamination, for example, through generation of slime.
Furthermore, in the case of the technology disclosed in Japanese Laid-Open Patent Publication No. 2000-97447, the configuration of some air conditioners makes it difficult to uniformly irradiate the entirety of the drain pan with ultraviolet rays using a single ultraviolet ray lamp, and thus, a number of ultraviolet ray lamps are necessary. Therefore, there is a problem with this technology in that the cost for installing ultraviolet ray lamps and the operating costs both are high.
Under these circumstances, an antibacterial member 50, where a container 50A having a mesh structure is filled with an antibacterial agent 50B in granular form or pellet form, is generally used in such a state that the entirety is submerged in the drain water, as shown in FIGS. 23(a) and 23(b). The antibacterial agent 50B dissolves in the water and has pasteurizing effects. Water soluble glass carrying an inorganic antibacterial agent can be cited as a concrete example of the antibacterial agent 50B. In the case of this bacteriostatic structure, the antibacterial member 50 is replaced with a new antibacterial member 50 when the antibacterial agent 50B in the container 50A has been used up, after a certain period of time.
The antibacterial agent 50B has the minimum level of concentration required for gaining bacteriostatic effects. This minimum concentration differs depending on the type of antibacterial agent 50B used. Therefore, the initial amount (immersed amount) of the antibacterial agent is determined so that this minimum concentration can be ensured under the worst conditions (conditions that minimize the concentration of the eluted antibacterial agent) within the range of conditions for conventional use, and stable and effective bacteriostatic effects can be gained over the years that the antibacterial agent is used.
FIG. 24 shows the relationship between the years (time) of use of the antibacterial agent 50B and the concentration of the antibacterial agent 50B in drain water. As the years of use increases, the antibacterial agent 50B depletes, and the concentration of the antibacterial agent 50B lowers (see A-B in FIG. 24). Accordingly, a large amount of antibacterial agent is necessary, in order to have bacteriostatic effects over N years, because the initial amount of antibacterial agent must be the sum of the amount of antibacterial agent which ensures the minimum concentration required after N years and the amount of antibacterial agent depleted over N years.
When all of the antibacterial agent of the amount determined in this manner is used in such a state as to be submerged in drain water, as shown in FIG. 23(a), the amount of eluted antibacterial agent 50B is high, and thus, effective bacteriostatic effects are gained, but the concentration of the antibacterial agent is higher than required, and the antibacterial agent is consumed in a wasteful manner.
In addition, though in the case where the period of use is short, only just the sufficient amount of antibacterial agent for ensuring the minimum concentration is required, it is necessary to increase the amount of antibacterial agent by such an amount that bacteriostatic effects can be gained over a long period of time (for example several years to a dozen or so years). In this case, the above described initial concentration is much greater than the above described minimum concentration required, and a problem arises that the antibacterial agent is consumed in a wasteful manner.